The invention relates to an inductive safety sensor for monitoring doors and gates and, more particularly, of elevators and/or lifts.
Two-channel inductive safety sensors are used for monitoring electrically and mechanically actuated revolving doors, sliding doors, rolling gates, flaps and hatches. Safety sensors ensure a secure monitoring of the open and closed position of doors and gates. Whereas commercially available inductive proximity switches can be actuated by means of virtually all metallic objects, the invention starts with the idea of further developing the proximity switch such that it emits a signal only by means of an especially constructed actuating element. It is an object of the invention to provide such an inductive proximity switch which has a constructively simple design.
The invention achieves this task by a safety sensor for monitoring the condition of doors and gates, particularly of elevators, that has a sensor device, which emits a signal only when sensing a target made of a defined material and switches from a first constant current to another constant current.
In contrast to the single-channel mechanical safety switches of the prior art, the safety sensors according to the invention, in particular, have the following advantages:
The sensor and the target operate in a contactless manner.
No mechanical wear occurs as a result of friction or burn-up at the contacts.
The sensor and the target can have a two-channel construction.
The sensor and the target can be mutually adapted. As a result of suitable measures, it can be ensured that a manipulation by foreign targets (non-ferrite) is excluded. A manipulation by magnets, jumpers and similar materials is, therefore, not possible. An internal signal evaluation takes place by way of interference-immune phase demodulation.
Protection Type IP67 can be implemented.
Several switch points can be securely monitored.
Changes of the distance between the sensor and the target by material fatigue are detected and are reported by the safety bus system to, for example, a control unit (preventive maintenance).
As a result of the linkage to a safety bus system, such as the applicant""s (CAN OPEN SAFETY), the output signals are monitored in a redundant manner. The signal transmission to the bus node takes place by interference-immune current loops.
The fastening of the safety sensor can take place in a simple manner by thread bolts or internal threads.
According to a variant, a balancing of the operating data of the sensor (switching interval) can be implemented by an advantageously uncomplicated construction of the sensor coil.
According to an embodiment, the sensor reacts only to ferrite, for example, and, in the event of a detection, switches from one constant current to another constant current. This permits line monitoring because operating currents other than the defined currents indicate a cable interference.
For safety-related reasons, the sensor has a redundant construction; that is, each sensor housing contains two sensor systems which are mutually, completely separated, with the exception of the positive supply voltage. The two systems are identical, with the exception of the excitation frequency, which must differ slightly in order to prevent a mutual influencing. In the further course, only one system which therefore be discussed.
Other aspects of the present invention will become apparent from the following detailed description of the invention, when considered in conjunction with accompanying drawings.